辫状河现代沉积研究与相模式──中国永定河剖析

永定河是一条多河型河流，自上而下，包括了辩状河→曲流河→分流网状河的河型空间转换。其间辫状河段可明显区分为两类亚型:即冲积扇区的高坡降辫状河和冲积平原区低坡降辫状河。二者在河流形态、沉积物特征等方面显示不同。而沉积作用机制和砂体沉积模式是近似的，二者均进行垂向加积作用，均发生五个级次的沉积再作用面，均发育三个级次类型的薄夹层:滞留层、落淤层、颗粒降纹层与颗粒流纹层。其中落淤层最具指相意义。在河道经常摆动迁移过程中，最终形成砂体广泛展布的“叠覆泛砂体”。这种辫状河沉积模式──“叠覆泛砂体”为油气储集提供了良好的储集空间和场所。

Study on Modern Deposit of a Braided Stream and Facies Model-Taking the Yongding River as an Exampl e

There are multipatterns in the Yongding River and they transfer from the braided to meandering,then to an abranched channel along the flow direction. The braided stream segment can be subdivided into two types: One is a high slope braided river which is distributed in the fluvial fan, another is a low slope braided river which is distributed in the fluvial plain. Both of them are different in river shape and sediment characteristics I but have similar sedimentation mechanism and models. There are five sedimentary reworking surfaces f and three types of thin interlayers, and they both have vertical accretion. The three thin interlayers are lag deposit,fall-siltseam and grain-fall lamina or grain flow lamina. The fall-siltseam is an important factes index. The wide-scale stacked pan-sandbody was formed by channel shifting. The braided stream sedimentation model-stacked pan-sndbody provides a good reservoir space for oil and gas.